Hi Alex, Thank you very much for your support. I pasted testing circuit again below; The AC noise is seen at the digital output of ADS1248 when inputing 0mV differential. The digital code is around 50uVp-p max and fluctuated. The application is thermocouple measurement equipment and use R6161 DC voltage generator at manufacturing test. The 1Mohm at INA129 input is for another voltage test purpose which actually 1Mohm is consisted of two registers to divide voltage. The grounding from VIN of INA129 is for bias current return. I am not sure if this should not be connected to ground but through resistance (like 10k, 40k or 1MHom). Please advise if so. And the 1uF cap between VREFOUT and VREFCOM is recommended to 1uF-47uF in d/s. We know the following solve the issue as a hint, - E1 and E0 are shorted. (but we have to isolate) - using another DC voltage generator than R6161. The R6161 generate output voltage using register(200ohm) divider and it has an load current impact. We are really not sure if the load current is change from ADS1210 to ADS1248 designs. Before INA129 circuit is exactly same for both. (we can not change R6161 to another DC voltage generator due to the customer fixed manufacturing system reason.) - ADS1210 does not have the issue. (we have to replace with ADS1248 or ADS124S06 ) - Decreasing D/R to 20SPS from 40SPS, the 50uVp-p is mitigated to 3uVp-p. In my first post, I wonder if this issue comes from CMRR? What is CMRR differences among three devices? ADS1210 (G=16, DR=55SPS, Turbo=1) ADS1248 (G=16, DR=40SPS) ADS124S06 (G=16, DR=50SPS, Sinc3, Chopper off) We are checking AVDD and DVDD ground layout and power supply without finding the error. Best regards, Masa
↧